The present invention relates to a plasma display device employing a plasma display panel (hereinafter referred to as a PDP) and a method of driving the PDP, and in particular is effective for improving ultraviolet-light-producing efficiency and thereby improving luminous efficacy.
Recently, quantity production of plasma display devices employing the ac surface-discharge type PDP has been started for use as large-area, thin-profile, color display devices. The ac surface-discharge type PDP is driven by ac voltages for generating surface-discharge.
FIG. 7 is an exploded perspective view of an example of a conventional ac surface-discharge type PDP employing a three-electrode structure.
In the ac surface-discharge type PDP shown FIG. 7, a discharge space 33 is formed between a pair of opposing glass substrates, a front substrate 21 and a rear substrate 28. The discharge space 33 is filled with a discharge gas at several hundreds or more of Torrs. As the discharge gas, usually He, Ne, Xe, and Ar are used either alone or in combination with one or more of the others.
A plurality of pairs of X and Y electrodes for sustaining discharge (hereinafter called discharge-sustaining electrodes or sustain-discharge electrodes) are disposed on the underside of the front substrate 21 serving as a display screen, for discharge-sustaining mainly for light emission for forming a display.
In this specification, xe2x80x9cdischarge-sustainingxe2x80x9d and xe2x80x9csustain-dischargexe2x80x9d are used interchangeably.
Usually, each of the X and Y electrodes is made of a combination of a transparent electrode and an opaque electrode for supplementing conductivity of the transparent electrode.
The X electrodes are comprised of transparent X electrodes 22-1, 22-2, . . . and corresponding opaque X bus electrodes 24-1, 24-2, . . . , respectively, and the Y electrodes are comprised of transparent Y electrodes 23-1, 23-2, . . . and corresponding opaque Y bus electrodes 25-1, 25-2, . . . , respectively. It is often that the X electrodes are used as a common electrode and the Y electrodes are used as independent electrodes.
A discharge gap Ldg between the X and Y electrodes in one discharge cell are designed to be small such that a discharge start voltage is not excessively high, and a spacing Lng between two adjacent cells is designed to be large such that unwanted discharge is prevented from occurring between two adjacent cells.
The X and Y sustain-discharge electrodes are covered with a front dielectric substance 26 which, in turn, is covered with a protective film 27 made of material such as magnesium oxide (MgO).
The MgO protects the front dielectric substance 26 and lowers a discharge start voltage because of its high sputtering resistance and high secondary electron emission yield.
Address electrodes 29 for addressing cells and thereby generating address-discharge are arranged on the upper surface of the rear substrate 28 in a direction perpendicular to the X and Y sustain-discharge electrodes.
The address electrodes 29 are covered with a rear dielectric substance 30, separation walls 31 are disposed between the address electrodes 29 on the rear dielectric substance 30.
A phosphor 32 is coated in a cavity formed by the surfaces of the separation walls 31 and the upper surface of the rear dielectric substance 30.
In this configuration, an intersection of a pair of sustain-discharge X, Y electrodes with an address electrode 29 corresponds to one discharge cell, and the discharge cells are arranged in a two-dimensional fashion. In a color PDP, a trio of three discharge cells coated with red, green and blue phosphors, respectively, forms one pixel.
FIG. 8 and FIG. 9 are cross-sectional views of one discharge cell shown in FIG. 7 viewed in the directions of the arrows D1 and D2, respectively. In FIG. 9, the boundary of the cell is approximately represented by broken lines. In FIG. 9, reference numeral denote electrons, 4 is a positive ion, 5 is a positive wall charge, and 6 are negative wall discharges.
Next operation of the PDP of this example will be explained.
The principle of generation of light by the PDP is such that discharge is started by a voltage pulse applied between the X and Y electrodes, and then ultraviolet rays generated by excited discharge gases are converted into visible light by the phosphor.
FIG. 10 is a block diagram illustrating a basic configuration of a plasma display device. The PDP 100 is incorporated into the plasma display device 102. A driving circuit 101 receives signals for a display image from a video signal source 103, converts the signals into driving voltages, and then supplies them to respective electrodes of the PDP 100. Concrete examples of the driving voltages are illustrated in FIGS. 11A-11C.
FIG. 11A is a time chart illustrating a driving voltage during one TV field required for displaying one picture on the PDP shown in FIG. 7. FIG. 11B illustrates waveforms of voltages applied to the address electrode 29, the X electrode and the Y electrode during the address-discharge period 50 shown in FIG. 11A. FIG. 11C illustrates pulse driving voltages (or voltage pulses) applied to the X and Y electrodes serving to sustain discharge and a driving voltage applied to the address electrode, all at the same time during the light-emission period 51 shown in FIG. 11A.
Portion I of FIG. 11A illustrates that one TV field 40 is divided into sub-fields 41 to 48 having different numbers of light emission more than one from one another. Gray scales are generated by a combination of one or more selected from among the sub-fields.
Suppose the eight sub-fields are provided which have gray scale brightness steps in binary number step increments, then each discharge cell of a three-primary color display device provides 28(=256) gray scales, and as a result the three-primary color display device is capable of displaying about 16.78 millions of different colors.
Portion II of FIG. 11A illustrates that each sub-field comprises a reset-discharge period 49 for resetting the discharge cells to an initial state, an address period 50 for addressing discharge cells to be selected and made luminescent, and a light-emission period (also called a sustain-discharge period) 51.
FIG. 11B illustrates waveforms of voltages applied to the address electrode 29, the X electrode and the Y electrode during the address-discharge period 50 shown in FIG. 11A. A waveform 52 represents a voltage V0(V) applied to one of the address electrodes 29 during the address-discharge period 50, a waveform 53 represents a voltage V1(V) applied to the X electrode, and waveforms 54 and 55 represent voltages V21(V) and V22(V) applied to ith and (i+1)st Y electrodes.
As shown in FIG. 11B, when a scan pulse 56 is applied to the ith Y electrode, in a cell located at an intersection of the ith Y electrode with the address electrode 29 supplied with the voltage V0, first an address-discharge occurs between the Y electrode and the address electrode, and then between the Y electrode and the X electrode. No address-discharges occur at cells located at intersections of the X and Y electrodes with the address electrode 29 at ground potential.
The above applies to a case where a scan pulse 57 is applied to the (i+1)st Y electrode.
As shown in FIG. 9, in the cell where the address-discharge has occurred, charges (wall discharges) are generated by the discharges on the surface of the dielectric substance 26 and the protective film 27 covering the X and Y electrodes, and consequently, a wall voltage Vw(V) occurs between the X and Y electrodes. In FIG. 9, reference numeral 3 denote electrons, 4 is a positive ion, 5 is a positive wall charge, and 6 are negative wall charges. Occurrence of sustaining discharge during the succeeding light-emission period 51 depends upon the presence of this wall charge.
FIG. 11C illustrates pulse driving voltages (or voltage pulses) applied to the X and Y sustain-discharge electrodes serving to sustain the discharge and a driving voltage applied to the address electrode, all at the same time during the light-emission period 51 shown in FIG. 11A.
The Y electrode is supplied with a pulse driving voltage of a voltage waveform 58, the X electrode is supplied with a pulse driving voltage of a voltage waveform 59, the magnitude of the voltages of the waveforms 58 and 59 being V3(V).
The address electrode 29 is supplied with a driving voltage of a voltage waveform 60 which is kept at a fixed voltage V4 during the light-emission period 51. The voltage V4 may be selected to be ground potential.
The pulse driving voltage of the magnitude V3 is applied alternately to the X electrode and the Y electrode, and as a result reversal of the polarity of the voltage between the X and Y electrodes is repeated.
The magnitude V3 is selected such that the presence and absence of the wall voltage generated by the address-discharge correspond to the presence and absence of the sustaining discharge, respectively.
In the discharge cell where the address-discharge has occurred, discharge is started by the first voltage pulse applied to one of the X and Y electrodes (the pulse 58A applied to the Y electrode in FIG. 11C), and the discharge continues until wall charges of the opposite polarity accumulate to some extent. The wall voltage accumulated due to this discharge serves to reinforce the second voltage pulse applied to the other of the X and Y electrodes (the pulse 59A applied to the X electrode in FIG. 11C), and then discharge is started again.
The above is repeated by the third, fourth and succeeding pulses (in FIG. 11C, a pulse 58B applied to the Y electrode, a pulse 59B applied to the X electrode, and so on).
In this way, in the discharge cell where the address-discharge has occurred, sustain-discharges occur between the X and Y electrodes the number of times equal to the number of the applied voltage pulses and thereby emit light. On the other hand, the discharge cells do not emit light where the address-discharge has not occurred.
The above are the basic configuration of the usual plasma display device and a usual driving method thereof.
The following are some of principal conventional techniques for driving the plasma display panel.
(1) Japanese Patent Application Laid-Open No. P2001-504243A (laid open on Mar. 27, 2001, and corresponding to International publication number WO98/21706) aims at improving deterioration in operating margin as in a case where the width of discharge-sustaining pulses is narrow in the range of 1 xcexcs or less, by applying space-charge-controlling, non-discharge-generating pulses to at least one of a pair of electrodes and an address electrode during a discharge-sustaining period so as to produce a space charge before main discharge. However, the peak value of the space-charge-controlling, non-discharge-generating pulses is limited such that no self-sustaining discharge is generated.
(2) Japanese Patent Application Laid-Open No. Hei 11-143425 (laid open on May 28, 1999) generates short-period discharges between facing electrodes by applying positive narrow-width pulses to address electrodes simultaneously with application of ac voltage pulses on the sustain-discharge electrodes, and then produces main discharge by using the short-period discharges as their triggers. This configuration aims at the advantage that the driving voltage can be kept to a low voltage as in a usual discharge gap even when the discharge gap is increased. However, the positive narrow-width pulses are applied to the address electrodes simultaneously with application of ac voltage pulses on the sustain-discharge electrodes, and therefore this is not intended to generate pre-discharge prior to main discharge.
(3) Japanese Patent Application Laid-Open No. Hei 11-149274 (laid open on Jun. 2, 1999) discloses a configuration in which two or more third electrodes are provided to oppose a pair of first and second sustain-discharge electrodes in each of discharge cells, and during the sustain-discharge period, pulses are applied to the third electrodes which rise (voltages change in the positive direction) prior to sustain-discharge pulses applied to the first and second electrodes, and then fall rapidly (voltages change in the negative direction) after cessation of main discharge, so as to limit the peak value of discharge currents. This configuration aims at the advantage of reducing the cost of the driving circuit and reducing defective image displays. The object of this patent application is to quicken the main discharge and thereby reduce the peak value of the discharge currents.
(4) Japanese Patent Application Laid-Open No. 2001-5424 (laid open on Jan. 12, 2001) aims at improving efficiency by applying a pre-discharge voltage to a data electrode (an address electrode) prior to sustain-discharge between the sustain-discharge electrodes, and thereby generating pre-discharge (only between the facing electrodes) during the sustain-discharge period. However, this patent application does not intend to increase efficiency by utilizing the highly efficient discharge between the sustain-discharge electrodes as the predischarge.
At present, efficiency of the PDP is inferior to that of a cathode ray tube, and therefore improvement of the efficiency of the PDP is necessary for wide spread of the PDPs as TV receivers.
There is also a problem in that, in realization of a large-screen PDP, a current to be supplied to its electrodes increases excessively and the power consumption increases.
In order to increase the number of pixels and thereby increase the degree of definition of a display image, it is necessary to reduce the size of the discharge cells. In this case also, there is also a problem in that the luminous efficacy is reduced because of the reduction in ultraviolet-light-producing efficiency caused by the decrease of the discharge space.
Basically, the improvement of luminous efficacy of the PDP is essential for solving the above problems. The present invention provides a technique for improving luminous efficacy in the sustaining discharge by improvement in a driving method for the plasma display device employing the PDP.
The following explains briefly the summary of the representative ones of the present inventions disclosed in this specification.
In accordance with an embodiment of the present invention there is provided a method of driving a plasma display device having a plasma display panel including a plurality of pairs of first and second discharge-sustaining electrodes, a plurality of address electrodes arranged to intersect the plurality of pairs of first and second discharge-sustaining electrodes, a dielectric substance covering the plurality of pairs of first and second discharge-sustaining electrodes, and a plurality of discharge cells defined by the plurality of pairs of first and second discharge-sustaining electrodes and the plurality of address electrodes; the method including at least address-discharge period for addressing the plurality of discharge cells and thereby inducing address-discharge therein; and light-emission period for applying repetitive discharge-sustaining pulse voltages to at least one of the first and second discharge-sustaining electrodes such that the addressed ones of the plurality of discharge cells start and sustain main discharge depending upon the presence of the address-discharge to generate light for formation of a display wherein second repetitive pulse voltages are applied to the plurality of address electrodes to generate pre-discharge, the pre-discharge initially occurring between the address electrodes of the addressed ones of the plurality of discharge cells and one of the first and second discharge-sustaining electrodes of the addressed ones, and thereafter occurring between the first and second discharge-sustaining electrodes of the addressed ones, and the second repetitive pulse voltages rise in portions of the light-emission period during which an absolute value of a voltage difference between the pair of first and second discharge-sustaining electrodes does not exceed 0.9xc3x97a maximum of an absolute value of a voltage difference between the pair of first and second discharge-sustaining electrodes during the light-emission period.
In accordance with another embodiment of the present invention there is provided a method of driving a plasma display device including a plasma display panel having a plurality of discharge cells, each of the plurality of discharge cells being provided with a pair of discharge-sustaining electrodes, an address electrode disposed to intersect the pair of discharge-sustaining electrodes, and a dielectric substance covering the pair of discharge-sustaining electrodes; the method including at least address-discharge period for addressing the plurality of discharge cells and thereby inducing address-discharge therein; and light-emission period for applying repetitive discharge-sustaining pulse voltages to at least one of the first and second discharge-sustaining electrodes such that the addressed ones of the plurality of discharge cells start and sustain main discharge depending upon the presence of the address-discharge to generate light for formation of a display, wherein second repetitive pulse voltages are applied to the plurality of address electrodes to generate pre-discharge, the pre-discharge occurs at least during a portion of at least one of intervals of time, the pre-discharge initially occurring between the address electrodes of the addressed ones of the plurality of discharge cells and one of the first and second discharge-sustaining electrodes of the addressed ones, and thereafter occurring between the first and second discharge-sustaining electrodes of the addressed ones, where t1xe2x89xa6the interval of timexe2x89xa6t2, V3 is a maximum of an absolute value of a voltage difference between the first and second discharge-sustaining electrodes during the light-emission period, S1 periods are each defined as periods which straddle respective valleys of a waveform of the absolute value of the voltage difference, and during which the absolute value of the voltage difference is less than or equal to 0.9xc3x97V3, t1 is a time at which each of the S1 periods starts, S2 periods are each defined as periods during which the absolute value of the voltage difference is less than or equal to 0.5xc3x97V3 within a respective one of the S1 periods, and t2 is a time at which each of the S2 periods ends.
In accordance with another embodiment of the present invention there is provided method of driving a plasma display device including a plasma display panel having a plurality of discharge cells, each of the plurality of discharge cells being provided with a pair of discharge-sustaining electrodes, an address electrode disposed to intersect the pair of discharge-sustaining electrodes, and a dielectric substance covering the pair of discharge-sustaining electrodes; the method including at least address-discharge period for addressing the plurality of discharge cells and thereby inducing address-discharge therein; and light-emission period for applying repetitive discharge-sustaining pulse voltages to at least one of the first and second discharge-sustaining electrodes such that the addressed ones of the plurality of discharge cells start and sustain main discharge depending upon the presence of the address-discharge to generate light for formation of a display, wherein second repetitive pulse voltages are applied to the plurality of address electrodes to generate pre-discharge, the pre-discharge occurs during intervals of time, the pre-discharge initially occurring between the address electrodes of the addressed ones of the plurality of discharge cells and one of the first and second discharge-sustaining electrodes of the addressed ones, and thereafter occurring between the first and second discharge-sustaining electrodes of the addressed ones, where t1xe2x89xa6the interval of timexe2x89xa6t2, V3 is a maximum of an absolute value of a voltage difference between the first and second discharge-sustaining electrodes during the light-emission period, S1 periods are each defined as periods which straddle respective valleys of a waveform of the absolute value of the voltage difference, and during which the absolute value of the voltage difference is less than or equal to 0.9xc3x97V3, t1 is a time at which each of the S1 periods starts, S2 periods are each defined as periods during which the absolute value of the voltage difference is less than or equal to 0.5xc3x97V3 within a respective one of the S1 periods, and t2 is a time at which each of the S2 periods ends.
In accordance with another embodiment of the present invention there is provided a method of driving a plasma display device including a plasma display panel having a plurality of discharge cells, each of the plurality of discharge cells being provided with a pair of first and second discharge-sustaining electrodes, an address electrode disposed to intersect the pair of first and second discharge-sustaining electrodes, and a dielectric substance covering the pair of first and second discharge-sustaining electrodes; the method including at least address-discharge period for addressing the plurality of discharge cells and thereby inducing address-discharge therein; and light-emission period for applying repetitive discharge-sustaining pulse voltages to at least one of the pair of first and second discharge-sustaining electrodes such that the addressed ones of the plurality of discharge cells start and sustain main discharge depending upon the presence of the address-discharge to generate light for formation of a display, wherein an address voltage comprised of second repetitive pulse voltages is applied to the plurality of address electrodes to generate pre-discharge, the second repetitive pulse voltages changing in a positive direction during at least a portion of an interval of time, the pre-discharge initially occurring between the address electrodes of the addressed ones of the plurality of discharge cells and one of first and second the discharge-sustaining electrodes of the addressed ones, and thereafter occurring between the pair of first and second discharge-sustaining electrodes of the addressed ones, where t1xe2x89xa6the interval of timexe2x89xa6t2, V3 is a maximum of an absolute value of a voltage difference between the first and second discharge-sustaining electrodes during the light-emission period, S1 periods are each defined as periods which straddle respective valleys of a waveform of the absolute value of the voltage difference, and during which the absolute value of the voltage difference is less than or equal to 0.9xc3x97V3, t1 is a time at which each of the S1 periods starts, S2 periods are each defined as periods during which the absolute value of the voltage difference is less than or equal to 0.5xc3x97V3 within a respective one of the S1 periods, and t2 is a time at which each of the S2 periods ends.
In accordance with another embodiment of the present invention there is provided a plasma display device comprising: a plasma display panel including a plurality of pairs of first and second discharge-sustaining electrodes, a plurality of address electrodes arranged to intersect the plurality of pairs of first and second discharge-sustaining electrodes, a dielectric substance covering the plurality of pairs of first and second discharge-sustaining electrodes, a plurality of discharge cells defined by the plurality of pairs of first and second discharge-sustaining electrodes and the plurality of address electrodes; a pulse generating circuit having a voltage input terminal and a plurality of output terminals corresponding to the plurality of pairs of first and second discharge-sustaining electrodes and supplying pulses to the plurality of pairs of first and second discharge-sustaining electrodes for generating sustaining-discharge between the first and second discharge-sustaining electrodes, a driving circuit for selectively applying address-pulse voltages to the plurality of address electrodes of the plurality of discharge cells intended for formation of a display, and a control circuit for controlling pre-discharge pulse voltages such that the pre-discharge pulse voltages are applied to the plurality of address electrodes to generate pre-discharge for triggering the sustaining-discharge, the pre-discharge initially occurring between the address electrodes of the addressed ones of the plurality of discharge cells and one of the first and second discharge-sustaining electrodes of the addressed ones, and thereafter occurring between the first and second discharge-sustaining electrodes of the addressed ones, and the pre-discharge pulse voltages rise in portions of the light-emission period during which an absolute value of a voltage difference between the pair of first and second discharge-sustaining electrodes does not exceed 0.9xc3x97a maximum of an absolute value of a voltage difference between the pair of first and second discharge-sustaining electrodes during the light-emission period.
The configuration of the PDP itself used in the present invention is not limited to those illustrated below concretely, but other configurations of the PDP can be used. Plasma display panels are sufficient which are provided at least with a plurality of pairs of first and second sustain-discharge electrodes, a plurality of address electrodes arranged to intersect the pairs of first and second sustain-discharge electrodes, and a plurality of discharge cells formed at intersections of the pairs of first and second sustain-discharge electrodes and the address electrodes.